Carbon fibre has found widespread use in a variety of different applications as a consequence of its exceptional strength. For example, it is possible to form a yarn by twisting together a multiplicity of individual carbon fibres, and this yarn may, for instance, be woven into a fabric. Alternatively, the carbon fibre yarn may be combined with any of a number of plastics materials and wound or moulded to form a composite material such as a carbon fibre reinforced polymer; such materials have particularly high strength to weight ratios.
Carbon fibre also has the advantage of considerably lower density when compared with steel, and this makes it an ideal material for applications requiring low weight. The properties of carbon fibre, such as high tensile strength, low weight and low thermal expansion, make it especially useful in aerospace, civil engineering, military, and motor sports applications. However, it is in carbon fibre reinforced polymers that the material finds the most widespread use.
A great deal of prior art exists which details the preparation and use of carbon fibre-based materials. However, some drawbacks are associated with the use of such materials. Cost, for example, can be an issue in certain applications. Furthermore, at the end of their useful lives, many materials which comprise carbon fibres are currently disposed of at landfill sites, thereby adding to the global problems of waste disposal and creating further environmental problems.
The present inventors, therefore, have examined the possibility that such waste carbon fibre material might be recycled and put to further use, thereby generating lower cost materials and helping to avoid the problems of waste disposal which might otherwise arise. Surprisingly, it has been found that not only may these materials be efficiently recycled, but it is also possible to further process them so as to produce carbon fibre yarn which is especially useful in textile applications.
Whilst the prior art, as previously noted, includes many references to the production and uses of carbon fibre yarns, all of these applications require the use of virgin carbon fibre, i.e. material which is newly prepared for a particular application, and is generally supplied as a continuous filament. Prior art in which recycled materials are used is confined to the production of substrates such as discs and sheet materials. Thus, for example, EP-A-530741 discloses fibrous substrates for the production of carbon and/or ceramic fibre reinforced carbon and/or ceramic matrix composites, particularly friction discs, and methods of manufacture thereof. The possibility of offcut waste fibrous sheet material being recycled and reformed into a web useful in the manufacture of such composites is discussed.
Alternatively, WO-A-2007/058298 teaches a recycled composite material made from a waste product of an original composite material, wherein the original composite material comprises a matrix and a carbon fibre structure contained in the matrix, the carbon fibre structure having a three-dimensional network structure. The recycled composite material is produced by supplementing the waste product of the original composite material with a matrix which is same as, and/or different to, the matrix contained in the waste material, and then kneading the resulting mixture.
The prior art, however, is silent as to the possibility of providing carbon fibre yarn from recycled carbon fibre materials, and it is this deficiency that the present inventors seek to address. Whereas virgin carbon fibre yarn, commonly referred to as carbon fibre tow, comprises continuous filament material, the present invention is concerned with the production of carbon fibre yarn from discontinuous recycled carbon fibre materials. The materials which are produced show satisfactory strength and durability in a wide range of applications and are much cheaper to produce than counterpart materials made from virgin carbon fibre tow. In addition, the recycling of waste carbon fibre products in this way has considerable environmental benefits and has the potential to contribute significantly to the alleviation of waste disposal problems.